Lens used in LED light emitting device is mass-produced by mechanical molding such as injection molding. Such lens has been produced by a thermoplastic resin such as acrylic resin or polycarbonate resin. However, introduction of the LED light emitting device that operates at a higher power has raised the problem that the lens made of a thermoplastic resin is insufficient in resistance to heat and color change.
Recently, lead free solder is widely used. Lead free solder, however, melts at a temperature higher than the conventional solder, and typically, a temperature of 260° C. or higher is used for the soldering of the optical device to the substrate. When the soldering is conducted at such temperature, conventional thermoplastic lens experiences problems such as deformation and yellowing by the high temperature, and use of the lens becomes impossible.
In view of such situation, use of a silicone resin for the lens of LED and the like has been considered in many cases. However, in the case of a lens having a hollow structure, the lens formed from the conventional hard silicone lens material suffer from insufficiency in the impact strength while the lens formed from a soft rubber suffer from deformation which results in the loss of optical properties and stress on the interior LED chip, wire, and the like.
Such prior arts are JP-A 2000-231002 corresponding to U.S. Pat. No. 6,285,513 and JP-A 2004-221308.